1. Field of the Invention
The present invention relates to a method of controlling the speed changing operations of a synchromesh type automatic transmission and, more particularly, to a method of ensuring the smooth changing operations of the synchromesh type automatic transmission even if a load on the transmission upon synchronization during the speed changing operations is high.
2. Description of the Prior Art
In recent years, automatic transmissions have been extensively used with vehicles. One type of automatic transmissions, which has an inertia lock type synchronizer conventionally used with a manual transmission, i.e., a so-called "synchromesh type transmission," has its automatic speed changing operations controlled by the use of a hydraulic transmission actuator and an electronic control unit.
For these automatic speed changing operations, it is necessary to release a clutch to disconnect an engine and the transmission. While the clutch is being released, the driving force of the engine is not transmitted to the drive wheel or wheels of the vehicle so that the vehicle runs for a period by its own inertia. As the period while the clutch is disengaged continues, the driver may sense the powerless running state of his vehicle and may feel uncomfortable during the drive. In order to eliminate this uncomfortable feeling, it is necessary to shorten the period for which the clutch is released by performing the speed changing operations as soon as possible.
In order to shorten the speed changing operations, it is possible to design the transmission actuator so that it operates for a short time period. For this design, it is sufficient to increase the actuating force and shorten the operating period of the transmission actuator. If this actuator thus constructed has a strong operating force and a short operating period, however, there arises a problem that so-called "under-synchronization" occurs, making the gears noisy if the difference in the revolutions per minute (i.e., the r.p.m.) between speed positions before and after shifting, i.e., a load upon synchronization is large, as in skip-shifting (e.g., from second to fourth speeds).
In order to solve that problem, it is sufficient to use an actuator which can control the operating force and period in a variable manner in dependence upon the magnitude of the synchronization load. Despite this fact, an actuator designed to have a variable operating force is disadvantageous in that it is complicated, thus raising its production cost and requiring more space.